The present invention relates to contact lens manufacturing, and more particularly relates to improved apparatus and methods for blocking a contact lens button (also termed a contact lens blank or precursor) for machining operations which form the button into a wearable contact lens.
One common method of manufacturing contact lenses is lathing the lens from a cylindrical contact lens button. Contact lens buttons may be cut from rod stock or sheet material, or individually cast in cups using a curable liquid monomer. While it is possible to attach the button directly to the lathe chuck, this is not commonly done since the chuck of the lathe machine uses radial compression to hold the work piece in place for lathing, and as such could impart damaging forces to the optical characteristics of the button. The button is therefore more commonly mounted to one end of a separate metal pin or "block", the opposite end of the block being configured as a spindle for removable insertion into the chuck of the lathe. The button is typically adhered to the block with an adhesive or special type of wax called "pitch" (with the block thus commonly referred to as a "pitch block" in the art). While the block and button are turned, a concave (or "base") curve is lathed into the exposed end of the button opposite the adhered end. While still attached to the chuck and rotating, a second "ledge" cut may be made in the outer cylindrical surface of the button for facilitating subsequent alignment with the front curve block, this cut typically termed a "base curve reference". A "front curve" block is then removably secured to the lathed base curve surface while attempting to maintain axial alignment with the first "base curve" block which is then removed from the button. The front curve block is mounted to the lathe chuck for lathing the convex or front curve of the button to form the finished lens. Lens edging and polishing operations may also be performed on each surface of the lens prior to removal from each block.
The multiple mounting and removal operations of the button to and from the blocks during the entire lathing process consumes a significant amount of time and is prone to error, especially in maintaining the necessary axial alignment between the base curve block and the front curve block. If precise axial alignment between the base and front curve blocks is not maintained, an undesired prism may be introduced to the resultant lens which must then be scrapped. Also, removal of the base curve block prior to lathing the front curve of the lens sometimes requires the use of heat or mechanical force, another added cost to the manufacturing process.